This invention relates to a heat exchanger capable of being effectively used for heat exchange of a liquid metal-water system conducted in, for example, a liquid metal-cooled reactor in which a high-temperature heating medium and a low-temperature heating medium are not allowed to contact each other, and more particularly to a heat exchanger adapted to conduct heat exchange via an intermediate heating medium chemically inactive with respect to both the high-temperature heating medium and low-temperature heating medium.
In a liquid-metal cooled reactor using, for example, liquid sodium as a coolant, heat exchange is carried out between a sodium system in which high-temperature sodium is circulated and a water-vapor system. In such a heat exchanger, when the sodium and water contact each other due to damage to a heat exchanger tube, both the sodium and water react with each other violently to get into the danger of causing a disaster to occur.
As a means for preventing the sodium and water from immediately contacting each other even when damage to a heat exchanger tube occurs, a method of conducting heat exchange via a stable substance, which reacts with neither the sodium nor water, is proposed in, for example, Japanese Patent Laid-Open No. 53-131394A/1978.
In a heat exchanger concretely proposed in the above-described prior art, a heat exchanger tube is molded in the form of a double tube structure having an outer tube and an inner tube, and water (low-temperature heating medium) is passed through the inner tube with sodium (high-temperature medium) passed through a space on the outer side of an outer circumference of the outer tube. An annular portion between the inner tube and the outer tube is filled with a stable substance (intermediate heating medium) reacting with neither water nor sodium, for example, mercury, via which heat exchange is conducted.
According to the prior art heat exchanger described above, it has the effect of preventing, owing to the presence of the intermediate heating medium, the sodium and water from contacting each other immediately even when one of the outer tube and the inner tube of the doubly formed heat exchanger tube is damaged. However, since a clearance between the inner tube and the outer tube in the double tube structure is comparatively narrow, the possibility that the inner tube and the outer tube can be damaged simultaneously is large. Furthermore, since the quantity of the intermediate heating medium flowing through the annular clearance is small, the possibility that the double tube structure is damaged, causing the sodium and water to contact each other, cannot necessarily be eliminated sufficiently.
Moreover, since all the heat exchanger tubes are formed as double tube structures, the construction of the heat exchanger becomes complicated, and the manufacturing cost becomes high.
An object of the present invention is therefore to provide a heat exchanger having an intermediate heating medium, capable of reducing more greatly the possibility that sodium and water contact each other directly than the above-described prior art heat exchanger in which an outer tube and an inner tube are formed to a double tube structure with a clearance between the outer tube and the inner tube filled with an intermediate heating medium, having a simple heat exchanger tube structure as compared with the double tube structure, and capable of reducing the manufacturing cost.
The heat exchanger having an intermediate heating medium according to the present invention comprises a shell of the heat exchanger, a plurality of cylindrical partition tubes each of which has an annular space therein and is closed at both end portions thereof with annular walls, the cylindrical partition tubes being arranged concentrically in a mutually spaced manner in the shell, and helical coil-shaped heat exchanger tubes each of which is disposed in the annular space in the cylindrical partition tube. A high-temperature heating medium flows in the shell through clearances among the helically arranged multiple cylindrical partition tubes, a low-temperature heating medium flows in each of the helical coil-shaped heat exchanger tubes, and an intermediate heating medium chemically inactive with respect to both the high-temperature heating medium and the low-temperature heating medium and excellent in heat transferring performance is passed through each of the annular spaces in the cylindrical partition tubes.
According to the heat exchanger of the present invention having such a structure, the helical coil-shaped heat exchanger tube is disposed in each of the multiple cylindrical partition tubes having the annular space therein. Therefore, this heat exchanger is structurally simple and can reduce the manufacturing cost as compared with the prior art heat exchanger in which all of the heat exchanger tubes are formed into double tube structures each of which includes an outer tube and an inner tube.
Further, since it is not unnecessary that a clearance between the inner surface of the cylindrical partition tube and the helical coil-shaped heat exchanger tube be formed as narrowly as that between the outer tube and the inner tube of the prior art double tube structure, the interior of the cylindrical partition tube can be filled with a large quantity of intermediate heating medium. Therefore, the possibility that the high-temperature heating medium (for example, sodium) in the exterior of the cylindrical partition tubes and the low-temperature heating medium (for example, water) in the interior of the heat exchanger tubes contact each other can be reduced to an extremely low level even when any heat exchanger tube or cylindrical partition tube should be damaged.
Furthermore, since the intermediate heating medium having an excellent heat transferring performance is not only packed, but also constantly circulated in a fluidized state in the interior of the cylindrical partition tubes, the performance of transferring heat from the high-temperature heating medium to the low-temperature heating medium is not substantially spoiled.
In a preferred embodiment of the present invention, opposed inner surfaces of each of the cylindrical partition tubes are provided with a plurality of baffle plates so that the baffle plates on the opposed inner surface project alternately among the helical coil-shaped heat exchanger tubes. Owing to this arrangement, the intermediate heating medium flowing in the cylindrical partition tubes can be made to flow in a zigzag pattern. As a result, the effectiveness of the heat exchange between the high-temperature heating medium in the exterior of the cylindrical partition tubes and the low-temperature heating medium in the interior of the heat exchanger tubes conducted via the intermediate heating medium is further improved, and the heat transferring performance of the heating media can be improved.
In a more preferred embodiment of the present invention, spiral spacers are disposed in the clearances among the concentrically arranged multiple cylindrical partition tubes. Owing to this arrangement, a flow passage for the high-temperature heating medium between the multiple cylindrical partition tubes can be secured. As a result, the heat exchange between the high-temperature medium in the exterior of the cylindrical partition tubes and the intermediate heating medium in the interior thereof is carried out effectively, and the heat transferring performance of the heating media can be improved.